1. Field of the Invention
This invention relates to control systems and methods for automatic transmissions providing a plurality of gear reduction ratios, such as automatic mechanical transmission (i.e. "AMT's"). In particular, the present invention relates to control systems and methods for vehicle automatic mechanical transmission systems wherein gear selection and shift decisions are made and executed based upon measured and/or calculated parameters such as vehicle and/or output shaft speed, transmission input shift speed, engine speed, throttle position, rate of change of throttle position, rate of change of vehicle and/or engine speed and the like. More particularly, the present invention relates to a method for controlling a vehicle AMT system including sensing or detecting of a skid or wheel lock-up condition, responding to the detection of a skid condition and system recovery from a skid or wheel lock-up condition.
2. Description of the Prior Art
The use of automatic transmissions of both the automatic mechanical type utilizing positive clutches and of the planetary gear type utilizing frictional clutches is well known in the prior art as are control systems therefor. Electronic control systems utilizing discrete logic circuits and/or software controlled microprocessors for automatic transmissions wherein gear selection and shift decisions are made based upon certain measured and/or calculated parameters such as vehicle speed (or transmission output shaft speed), transmission input shaft speed, engine speed, rate of change of vehicle speed, rate of change of engine speed, throttle position, rate of change of throttle position, full depression of the throttle (i.e. "kickdown"), actuation of the braking mechanism, currently engaged gear ratio, and the like are known in the prior art. Examples of such automatic transmission control systems for vehicles may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,551,802; 4,527,447; 4,425,620; 4,463,427; 4,081,065; 4,073,203;; 4,253,348; 4,038,889; 4,226,295; 3,776,048; 4,208,929; 4,039,061; 3,974,720; 3,478,851 and 3,942,393, the disclosures of which are all hereby incorporated by reference.
Vehicle brake anti-skid or anti-lock systems are also well known in the prior art. Briefly, as locking-up or skidding of a vehicle's wheels will provide less than optimal stopping and control of a vehicle, it is desirable to sense actual or impending wheel lock-up and, if such wheel lock-up conditions are sensed, to allow the wheels to roll-up to vehicle speed prior to reapplying the vehicle brakes. Examples of anti-skid or anti-lock brake systems may be seen by reference to U.S. Pats. Nos. 3,767,270; 3,768,872; 3,854,556; 3,920,284; 3,929,382; 3,966,267 and 3,995,912, the disclosures of which are hereby incorporated by reference.
While the above referenced automatic or semi-automatic mechanical transmission (i.e. "AMT") control systems, and similar systems, are effective to control an automatic transmission by selecting a desired gear ratio which will tend to optimize the fuel economy and/or performance of the vehicle in view of the sensed parameters and/or commanding a shift into a selected gear ratio, such control systems were not totally acceptable as the predetermined programs, or control methods, utilized did not include logic to sense an actual or impending lock-up or skid condition (also referred to as wheel lock-up conditions) and/or did not modify the programs to provide optimal operation in view of detection of a wheel lock-up condition.
A wheel lock-up condition presents several problems related to control of a vehicle AMT system, these include the inertia of the engine and clutch on the wheels which may delay the wheels' ability to roll-up to vehicle speed, the circumstance that the value of the output shaft speed signal may not be indicative of vehicle speed during a skid which may cause the transmission system to undesirably attempt one or more rapid downshift and the requirement of providing the system with the ability to revalidate the output shaft speed signal as a true indication of vehicle speed at expected termination of a wheel lock-up condition.